WO2012003596A1

WO2012003596A1 - Adhesive with buffer system

Info

Publication number: WO2012003596A1
Application number: PCT/CH2011/000161
Authority: WO
Inventors: Emil Simmler-Bornhauser; Thomas Simmler-Caduff
Original assignee: Alfa Klebstoffe Ag
Priority date: 2010-07-09
Filing date: 2011-07-08
Publication date: 2012-01-12
Also published as: AU2011276933A1; CN103221469A; BR112013000514B1; CA2804724A1; US9150708B2; CN103221469B; JP5859524B2; EA201390083A1; EP2591046B1; AU2011276933B2; US20130123400A1; EP2591046A1; ZA201300213B; DK2591046T3; KR20130096699A; BR112013000514A2; EA022694B1; PL2591046T3; JP2013531105A

Abstract

An adhesive based on a polychloroprene dispersion is characterized in that a buffer system comprising at least one acid compound and glycerin is included in order to activate and stabilize the adhesive. A freeze-thaw stability of the adhesive is achieved by surprisingly high proportions of glycerin; however, a good initial adhesion is simultaneously ensured. The glycerin proportions range from 8 - 50 wt.%, preferably 14 - 40 wt.%, particularly preferably 22 - 30 wt.%. An organic acid is preferably used as the acid compound.

Description

H2011 / 000161

1

Adhesive with buffer system

Technical area

The invention relates to an adhesive based on a polychloroprene dispersion and to the use of a buffer system for activating and stabilizing an adhesive based on a polychloroprene dispersion. State of the art

At present, dispersion adhesives, in particular water-based and solvent-free adhesives based on polychloroprene (CR) are used in the foam-processing industry. With such adhesives, in particular different foam qualities for the purpose of producing mattresses, upholstered furniture, office chairs, car seats, etc. can be bonded. In addition, these adhesives but also for the production of other technical products, such. As insulation materials, suitable.

Typically, polychloroprene dispersions are specifically destabilized or activated to achieve sufficient initial adhesion. This is also called "breaking". For this purpose, acids have hitherto been used which bring about a lowering of the pH of the adhesive formulation.

In EP 0624 634 (ALFA adhesives AG) is proposed for lowering the pH boric acid. Boric acid is also mentioned in US Pat. No. 6,31,352 B1 (Alfa Klebstoffe AG). Glycerin is used as a "solvent" for the boric acid at high boric acid contents, EP 2 166 054 A1 (Wakol GmbH) describes amino acids such as glycine, asparagine or glycylglycine as well as glyoxal, which are used dissolved in water ,

A mixture of boric acid and an amino acid z. B. Glycine describes the US 6,086,997 (Patel Vijay).

Furthermore, DE 10 2008 045 805 A1 discloses the addition of gaseous CO ₂ as an acidic compound or a means for lowering the pH.

However, all these formulations have in common that a permanent lowering of the pH value is not given and thus occur in practice a number of problems. Ie. the formulated adhesives do not stick sufficiently after some time, or the stability of the formulation is not given, so that sporadically or in the whole Mix coagulum, which make the adhesive unusable. In known formulations, in particular the shear stability as well as the storage and transport stability are reaching their limits unsatisfactorily. This problem is exacerbated in addition in cold seasons at temperatures below 0 ° C, which increased during transport and storage of such products, such. As cold-protected transports to meet.

In this respect, it is possible to carry out the destabilization or activation of the adhesive formulations according to the two-component principle only shortly before use. However, this means an additional expense for the user, which should be avoided if possible.

There is therefore still a need for alternative adhesive formulations which do not have the abovementioned disadvantages as far as possible.

Presentation of the invention

The object of the invention is thus to provide an adhesive which immediately after application has the highest possible initial adhesion and at the same time is stable over the long term.

The solution of the problem is defined by the features of claim 1. According to the invention, the adhesive based on a polychloroprene dispersion contains a buffer system comprising at least one acidic compound and glycerin for activation and stabilization of the adhesive, glycerol accounting for 8-50% by weight of the total weight of the adhesive dispersion. %, preferably 14-40 wt .-%, particularly preferably 22-30 wt .-% having.

The polychloroprene dispersion is a polymer dispersion. By the term polymer dispersion is meant in particular a heterogeneous mixture of at least one polymer compound and a liquid. The polymer compound is dispersed as dispersed phase as finely as possible in the liquid as a dispersion medium. In other words, the polymer dispersion forms a suspension containing the Contains polymer compound in colloid form. Advantageously, the polymer dispersion is an aqueous polymer dispersion which, in particular, is free from organic solvents except for unavoidable impurities.

The combination with the buffer system according to the invention makes polychloroprene-based adhesives accessible which, compared with known formulations, have a much higher stability and at the same time have an excellent initial adhesion.

A buffer system as used herein refers to a mixture of at least two components comprising at least one acidic compound and glycerin which synergistically interact with the remaining components of the adhesive so that the adhesive has increased initial adhesion and improved stability compared to the polychloroprene dispersion , Accordingly, the proportion of the buffer system or the proportions of the at least one acidic compound and the glycerin in particular are selected so that an increased initial adhesion is achieved with simultaneously improved stability. In this case, the acidic compound preferably has a proportion of at least 0.01% by weight. A maximum proportion of acidic compound is in particular 10 wt .-%. The proportion of the acidic compound is partly determined by the acidity or the pK _s value of the acidic compound. The proportion of glycerol is advantageously at least 8% by weight. An advantageous maximum value of the proportion of glycerol is 50% by weight.

In this context, an acidic compound is understood as meaning a chemical compound which, in particular in the sense of a Bronsted acid, acts as a proton donor and / or in the form of a Lewis acid as an electrophilic electron acceptor. Likewise, however, the acidic compound may also be a substance which develops an acidic action by interacting with the other components of the adhesive. The acidic compound can be, for example, an organic-chemical, inorganic-chemical and / or organometallic compound. In principle, the acidic compound can be in solid, liquid and / or gaseous form or admixed. Unless stated otherwise, all statements relating to percentages by weight or% by weight of individual components of the adhesives according to the invention relate to the wet total weight of the usable or ready-to-use adhesive. The novel adhesives based on a polychloroprene dispersion and a buffer system comprising at least one acidic compound and glycerol exhibit, inter alia, surprisingly high initial adhesion values and have proved to be largely stable over the long term and under very different external conditions. In particular, higher storage, transport and processing stabilities can be realized with the adhesives of the invention. Accordingly, the adhesives according to the invention also have longer storage times, which entails additional flexibility in the processing of the adhesives.

This is surprising insofar as it was previously assumed that glycerol generally adversely affects the initial adhesion of adhesives. However, in comparison with adhesives which contain either only an acidic compound or only glycerol, the adhesives according to the invention show in particular an unexpectedly high stability with unchanged or improved initial adhesion.

Regarding stability, it has been shown that the decisive in practice adhesive properties such. For example, the initial adhesion, chemical composition, viscosity, or visual appearance may remain substantially constant for up to several months. This also makes it possible to use the novel adhesives as one-component systems, which considerably simplifies handling for the user.

In particular, the adhesives of the invention show a significant freeze-thaw stability. This means that the adhesive can be frozen and thawed again as far as possible without residue, while retaining its properties. The temperature at which a dispersion adhesive according to the invention can be cooled to a maximum depends on the proportion of glycerol. In the context of the invention, glycerol, based on the total weight of the wet adhesive, has a fraction of 8-50% by weight, preferably 14-40% by weight, particularly preferably 22-30% by weight. As has been shown, the adhesives according to the invention are freeze-thaw-stable and without their initial adhesion being noticeably impaired. This is particularly unexpected because it has been assumed that such unusually high levels of glycerin lead to a massive reduction in initial adhesion. In the context of the present invention, however, just the opposite was observed, which is likely to be due to the buffer system or the interaction of the acidic compound and the glycerin. Freeze adhesives with the above-mentioned proportions of glycerol, they can thaw residue free again. In addition, without the beneficial properties of the adhesives would suffer. On the contrary, the adhesives have the required initial adhesion immediately after thawing and can be used as intended. In other words, the inventive adhesives can be reversibly frozen and thawed again.

This property is particularly advantageous in terms of storage and transport of the adhesive. In hitherto known adhesives, which usually can not freeze and thaw without loss of quality, in particular the transport in cold seasons requires special measures, ie complex and therefore expensive thermal transports. This problem is completely eliminated with the adhesives according to the invention, which means that they can be expelled, inter alia, more economically.

A positive influence on the freeze-thaw stability can be found in glycerol contents of 8-50% by weight, based on the total weight of the adhesive dispersion. Higher levels of glycerol than 50% by weight are also possible, but provide no added benefit in terms of freeze-thaw stability. At levels less than 8% by weight of glycerin, the freeze-thaw stability decreases sharply. In this case, however, the improved stability in the temperature range above the freezing point is retained. Generally, with a decreasing glycerol content, the temperature, while still having a freeze-thaw stability is present, rises and generally migrates to 0 ° C. The less glycerine in the adhesive, the less freeze resistance this adhesive offers.

The proportion of glycerol is preferably 14-40% by weight. Particularly preferably, the adhesive consists of 22-30% by weight of glycerol. In these glycerol portions of the adhesive can be cooled several times to below -20 ° C and then thawed again, without changing its adhesive properties. In this most preferred range, the initial adhesion is good.

In a preferred embodiment, the adhesives according to the invention are correspondingly present as one-component adhesives. For special applications, however, it is in principle possible to design the adhesives as multicomponent systems.

In contrast to adhesives without the buffer system according to the invention, the adhesives according to the invention also have improved processabilities and machine running properties. Likewise, the inventive adhesives show faster drying or setting. Compared to known adhesives, which contain, for example, only one acid for activation, the required amount of acidic compound can also be reduced due to the inventive buffer system with the same initial adhesion, which has a positive effect on the manufacturing cost. This also illustrates the synergetic interaction between acidic compound and glycerol in the novel adhesives.

The inventive buffer system also works with a wide range of different acidic compounds and is correspondingly flexible. So it is z. B. secondary, in which form the at least one acidic compound is present. Even with polychloroprene dispersion, which are acted upon with gaseous C0 ₂ as an acidic compound, can be achieved by the addition of glycerol or the preparation of a buffer system according to the invention a significant stability improvements at high initial adhesion. The novel adhesives are also flexible and easy to process. Thus, the adhesives can be applied to a substrate to be bonded directly by means of spray nozzles, low-pressure spray guns, brushes, rolling units or the like without further pretreatment. A prior mixing of additional components is not necessary accordingly.

In conjunction with an acidic compound, glycerin has thus proved to be an advantageous buffer system for adhesives based on polychloroprene dispersions.

The polychloroprene dispersion preferably additionally comprises polyacrylates, in particular acrylic acid ester copolymers, styrene-acrylate copolymers and / or mixtures thereof. The polyacrylates are particularly advantageous in combination with polychloroprene as the main polymeric component and act as additional binders. In particular, the additional polyacrylates have a lower proportion than the main polymeric component. Due to the additional polyacrylates and in particular the mentioned representatives, both the initial and final adhesive values of the novel adhesives can be significantly increased and adapted to different substrates to be bonded.

But it is also possible to add other compounds to improve the adhesive properties instead of or in addition to polyacrylates.

It may also be advantageous if the polychloroprene dispersion additionally contains one or more polymer compounds from the series polyvinyl acetate, polyvinyl butyral and / or polyurethane. Also advantageous may be additional polymer compounds in the form of copolymers of vinyl acetate, ethylene vinyl acetate, vinyl butyral and / or urethane. These may in particular also be terpolymers.

The said additional polymer compounds are particularly advantageous in combination with polychloroprene as the main polymeric component and optionally additional polyacrylates. The presence of the additional polymer compounds improves in particular the adhesive properties and the resistance of the adhesives and allows a reduction of the manufacturing costs. An addition of additional polymer compounds, however, is not mandatory and may also be omitted, depending on the intended use of the adhesive.

In a preferred embodiment, the at least one acidic compound has a pK _s value of 2-10. The pK _s value is the negative decadic logarithm of the equilibrium constant K _{s of} the acidic compound in water at a temperature of 25 ° C. As has been shown, such acidic compounds in combination with glycerol give particularly effective buffer systems for a variety of polychloroprene dispersions of interest. As a result, both the initial adhesion and the stability of the adhesives according to the invention are generally improved significantly. Furthermore, acid compounds with a pK _s value of 2-10 can be well dosed during adhesive production.

In principle, however, it is also possible to use acidic compounds having a pK _s value of less than 2 or more than 10. This may even be advantageous for specific adhesives and / or specific applications. Optionally, it is also possible to provide, in addition to at least one acidic compound having a pK _s value of 2-10, one or more further acidic compounds which need not necessarily have a pK _s in the range 2-10.

Most preferably, the at least one acidic compound comprises a proton donor. In particular, the at least one acidic compound comprises citric acid (pK _s1 = 3.13, pK _S2 = 4.76, pK _S3 = 6.4), tartaric acid (pK _s1 = 2.98, pK _S2 = 4.34), ascorbic acid (pK _s = 4.25), maleic acid or its anhydride (pK _s1 = 1.9, pK _S2 = 6.5), malic acid (pK _s1 = 3.46, pK _S2 = 5.10), amino acids such. For example, glycine (ρΚ _0ΟΟΗ ⁼ 2.35, pK _NH2 = 9.78), monosodium dihydrogen phosphate (pK _s1 = 7.2, pK _S2 = 12.32) and / or carbonic acid (pK _s1 = 6.35, pK _S2 = 10.33). It is also possible that two or more representatives of said acidic compounds are used in combination. When using such compounds in combination with glycerol, the advantages according to the invention, ie a high initial adhesion combined with improved stability, are particularly pronounced Appearance. In addition, it has been found that the said acidic compounds are largely compatible with a large number of other adhesive components.

In principle, however, other acidic compounds can be provided instead of or in addition to the abovementioned representatives. This can z. B. Lewis acids and / or CH-acidic organic compounds.

The at least one acidic compound advantageously has a proportion of 0.01-10% by weight, in particular 0.1-1.5% by weight, based on the total weight of the adhesive dispersion. Such proportions, in combination with glycerol, give an optimal effect of the buffer system in the adhesive. This is especially true in connection with a content of glycerol of 8-50 wt .-%, preferably 14- 40 wt .-%, particularly preferably 22-30 wt .-% to. In this case, adhesives with unexpectedly high initial bond strengths and freeze-thaw stabilities can be realized.

However, the at least one acidic compound may in principle also have lower proportions than 0.01% by weight or higher than 10% by weight. In general, however, in this case the advantages according to the invention decrease.

An advantageous weight ratio of glycerol to at least one acidic compound is in the range from 0.8 to 500, in particular 5 to 300, more preferably 10 to 100. As a result, an optimally functioning buffer system is obtained. In principle, however, it is also possible to prepare adhesives according to the invention with other weight ratios. A pH of the adhesive is advantageously in the range of 5-9, more preferably in the range of 7-9. Such a pH is particularly optimal in order to achieve a high initial adhesion with simultaneous stability.

However, it is basically possible to provide adhesives with lower or higher pH values. According to further preferred embodiments, the adhesives according to the invention optionally contain at least one emulsifier, where the at least one emulsifier is in particular a polyglycol ether, sodium lauryl sulfate and / or ethyl vinyl ether / maleic anhydride. acid anhydride copolymer. By such emulsifiers, the stability of the adhesives can be further increased and at the same time improve the processability.

In principle, such emulsifiers can also be omitted or replaced by other emulsifiers. More preferably, the adhesive according to the invention contains an optional plasticizer, in particular one or more representatives from the series Acetyltributylcitrat, benzoates and / or Terephtalsäuredialkylester. As has been shown, the plasticizers mentioned are in particular compatible with the buffer system according to the invention, without impairing the stability or initial adhesion. Advantageously, the plasticizer has a proportion of 0.1 to 20 wt .-%, in particular 0.1 to 10 wt .-%, preferably 0.5 to 5 wt .-%, more preferably 1 - 2 wt .-%. The plasticizers make flexible films applied to a substrate more flexible, which, for example, increases the plastic adhesion.

In principle, plasticizers are not absolutely necessary. Accordingly, it can be dispensed with.

Furthermore, it may be advantageous to add fillers to the adhesive. It is preferably CaC0 ₃ , ZnO, MgO, Ti0 ₂ , ZrO _z and / or talc. As a result, among other things, the production costs can be reduced. However, such fillers are optional and may optionally be omitted or replaced by other fillers. Furthermore, the adhesives of the invention may optionally comprise one or more additional components from the series thickeners, dyes, wetting agents, resins, UV absorbers, defoamers and / or biocides. This allows the adhesives to be adapted to specific requirements or environmental influences.

Particularly suitable thickeners are z. As aqueous dispersions of methyl vinyl ether / maleic anhydride copolymers. From the following detailed description and the totality of the claims, further advantageous embodiments and feature combinations of the invention result.

Modes for Carrying Out the Invention 1. Polychloroprene based adhesive

Table 1 shows a first adhesive composition according to the invention. All parts by weight are based on the wet total weight of the ready-to-use adhesive. The polychloroprene dispersion used is Dispercoll C84 (Bayer MaterialScience), an aqueous-colloidal dispersion of a polymer of 2-chlorobutadiene. The dispersion contains about 55% by weight of polymer in H ₂ O. The buffer system consists of glycerol (weight fraction 23.56% by weight, first buffer component) and ascorbic acid (0.75% by weight, pK _s = 4.25; ) as an acidic compound. The weight ratio of glycerol to ascorbic acid is about 31. The pH of the adhesive is about 8.0. On the one hand, methyl vinyl ether / maleic anhydride copolymers (MVE / MA copolymers, 0.5% solutions in H ₂ O) are present as emulsifiers. On the other hand, a 30% solution of sodium lauryl sulfate in H ₂ 0 is used. In addition, a sodium salt of a sulfated fatty alcohol ethoxylate is used.

Furthermore, the first adhesive according to the invention contains Agitan 305 as defoamer and 0.31% by weight of water for dilution.

To prepare the adhesive composition of Table 1, the components mentioned are mixed together in a conventional manner.

Table 1

Component weight percentage function

in %

Polychloroprene dispersion (CR, eg, 60.47 polymer base; Dispercoll C84; 55% polymer content in binder

H ₂ 0)

Glycerine 23.56 1. Buffer component

Ascorbic acid 0.75 2. buffer component

MVE / MA copolymer (0.5% in H ₂ O) 10.99 emulsifier

Sodium Lauryl Sulfate (30% in H ₂ O) 1.31 Stabilizer

Agitan 305 0.04 defoamer

Water 1.31 dilution

Sodium salt of a sulfated 1.57 emulsifier

fatty alcohol ethoxylate

Test experiments with the first adhesive dispersion according to the invention have shown a storage stability at room temperature in the range from 6 to 8 months. In addition, the adhesive dispersion is largely stable to frost. Although the dispersion freezes at temperatures below 0 ° C or solidifies, but can be thawed several times residue-free and is then reused as intended.

Furthermore, the first adhesive dispersion according to the invention has a high initial adhesion or immediate adhesion after the application of adhesive. As a result, in particular foam substrates can be further processed directly after joining, without the risk that move the joined parts. In the case of foam bonding, the initial adhesion when using the first adhesive according to the invention is generally so high that, given a corresponding load, the bonded foam substrates are destroyed before the adhesive layer.

2. Polychloroprene-Based Adhesive Table 2 shows the composition of a second adhesive according to the invention. All parts by weight are again based on the wet total weight of the ready-to-use adhesive. As the polychloroprene dispersion, Dispercoll C84 (Bayer MaterialScience) is also used here. The buffer system consists of glycerine (weight fraction 29.30% by weight, 1st buffer component) and citric acid (0.27% by weight, pK _s1 = 3.13, pK _S2 = 4.76, pK _S3 = 6.4; 2nd buffer component) as an acidic compound. The weight ratio of glycerin to citric acid is about 109. The pH of the adhesive is about 8.1.

As emulsifiers methyl vinyl ether / maleic anhydride copolymers (MVE / MA copolymers, 0.5% solutions in H ₂ 0), sodium lauryl sulfate (30% solution in H ₂ 0) and Acetyltributylcitrat used.

To set the correct viscosity, Mowidick EMS 6 is used as thickener, 0.10% by weight of water for dilution and Dispercoll S 5005, an aqueous anionic colloidally disperse solution of amorphous silicon oxide.

The adhesive with the composition according to Table 2 is prepared from the enumerated components in a conventional manner by mixing.

Table 2

The properties of the second inventive adhesive dispersion in terms of storage stability at room temperature and the freeze-thaw stability are comparable to those of the first inventive adhesive dispersion. Also has the second Adhesive dispersion according to the invention over a high initial adhesion or immediate adhesion after the adhesive application.

3. Polychloroprene based adhesive

Table 3 shows a third adhesive composition according to the invention. The polychloroprene dispersion used is Dispercoll C84 (Bayer MaterialScience) with about 55% by weight of polymer in H ₂ O. The buffer system consists of glycerin (weight fraction 29.5% by weight, 1st buffer component) and citric acid (0.3% by weight, pK _s1 = 3.13, pK _S2 = 4.76, pK _S3 = 6.4, 2nd buffer component) as the acidic compound. The weight ratio of glycerine to citric acid is about 98. The pH of the adhesive is about 8. Furthermore, the adhesive contains thickener for adjusting the viscosity. For this purpose is z. For example, an aqueous anionic colloidally disperse solution of amorphous silica (eg, Dispercoll S 3030, Bayer MaterialScience) is provided in combination with aqueous dispersions of methyl vinyl ether / maleic anhydride copolymers (eg, Mowilith EMS 6, Celanese Emulsions, about 6% solids). On the one hand, methyl vinyl ether / maleic anhydride copolymers (MVE / MA copolymers, 0.5% solutions in H ₂ O) are present as emulsifiers. On the other hand, a 30% solution of sodium lauryl sulfate in H ₂ 0 is used.

Furthermore, the third adhesive according to the invention contains acetyltributyl citrate as plasticizer and a biocide based on chloromethyl / methylisothiazolone and bronopol. The latter is available, for example, under the name Rocima 520 from Rohm and Haas.

Table 3

Component weight percentage function

in %

Polychloroprene dispersion (CR, eg 53.1 polymer base;

Dispercoll C84; 55% polymer content in binder

H ₂ 0)

Glycerine 29.5 1st buffer component

Citric acid (powder) 0.3 2. Buffer component Colloidal silica solution 2.0 thickener

(eg Dispercoll S 3030, about 30%

Solids content in H ₂ 0)

Mowilith EMS 6 0.3 thickener

Sodium lauryl sulfate (30% in H ₂ O) 1.9 Emulsifier, stabilizer

MVE / MA copolymer (0.5% in H ₂ O) 1 1.2 Emulsifier

Acetyltributyl citrate 2.0 plasticizer

Biocide based on chloromethyl / methyliso-0.1 preservation

thiazolone and bronopol (eg Rocima

520)

The third adhesive dispersion according to the invention also has all the mentioned advantageous properties.

4. Polychloroprene Based Adhesive Table 4 shows an example of an adhesive having a slightly lower glycerin content. The frost-thaw stability of this adhesive is somewhat reduced compared to the first three examples. The adhesive can be safely used at minus temperatures down to about -10 ° C.

Table 4

Component weight percentage function

in %

Polychloroprene dispersion (CR, eg, 49.63 polymer base;

Dispercoll C84; 55% polymer content in binder

H ₂ 0)

Glycerol 16.54 1st buffer component

Citric acid 0.3 2. buffer component

Dispercoll S 5005 0.35 viscosity adjustment

Sodium Lauryl Sulfate (30% in H ₂ O) 0.96 Stabilizer

MVE / MA copolymer (0.5% in H ₂ O) 9.58 Emulsifier

Acetyltributyl citrate 0.35 plasticizer

Sodium salt of a sulfated 0.52 emulsifier fatty alcohol ethoxylate

Water 21.77 dilution

5. Polychloroprene based adhesive

Table 5 shows an example of a polychloroprene-based adhesive with an increased glycerol content of about 37% by weight. This adhesive has a particularly good freeze-thaw stability (below -20 ° C), even if it dries slower compared to Examples 1-3.

Table 5

6. Polychloroprene- and Acrylate-Based Adhesive Table 6 gives a sixth adhesive composition according to the invention. All parts by weight in turn relate to the wet total weight of the ready-to-use adhesive. As the polychloroprene dispersion, as in the case of the other adhesives according to the invention, Dispercoll C84 (Bayer MaterialScience) is used. In addition, there is an acrylate dispersion. In the latter, it is z. For example, Acronal S 600 from BASF; which has about 50% acrylate in H ₂ 0. The buffer system consists of a glycerol solution (8.50% by weight, 1st buffer component) and citric acid (0.37% by weight, pK _s1 = 3.13, pK _S2 = 4.76, pK _S3 = 6.4; 2nd buffer component) as an acidic compound. The weight ratio of glycerol to citric acid is about 23.

Furthermore, the sixth inventive adhesive contains the stabilizer sodium lauryl sulfate (30% in H ₂ 0), MVE / A copolymers (0.5% in H ₂ 0) and acetyltributyl citrate as emulsifiers and Dispercoll S 5005 for viscosity adjustment. The pH of the adhesive is about 8.4.

Table 6

The sixth inventive adhesive has a limited frost stability at temperatures down to -5 ° C. Tests for storage stability at room temperature and for initial adhesion have shown substantially the same results as with the polychloroprene-based adhesive dispersions.

7. Polychloroprene and acrylate based adhesive

Table 7 represents a seventh adhesive composition according to the invention, the basis of which is formed from polychloroprene and acrylate. The buffer system consists of a glycerol solution (86.5% glycerol in H ₂ O, 1st buffer component) and citric acid (2.3% by weight). %; pK _s = 9.14; 2nd buffer component) as an acidic compound. The proportion by weight of pure glycerin in the adhesive is corresponding to about 16.7 wt .-%. The weight ratio of glycerol to citric acid is about 7. Furthermore, the seventh adhesive according to the invention contains acetyltributyl citrate as plasticizer and Mowilith EMS 6 as thickener. The pH of the adhesive is about 7.5.

Table 7:

Test experiments with the seventh adhesive dispersion of the invention have given substantially the same results as with the first three adhesive dispersions. Due to the high proportion of glycerol, the frost-thaw stability of the adhesive is ensured even at temperatures down to -20 ° C.

Comparative tests

For comparative purposes, several further tests were performed. In a first series of comparative experiments, glycerol as buffer component was omitted from the formulations of the adhesive dispersions according to the invention. The storage stabilities have worsened significantly. Glycerine-free adhesive dispersions tend to coagulate within a few days or weeks and become unusable. Furthermore, the adhesive dispersions without glycerin are not stable to frost. During thawing, residues were consistently observed, which affected the quality of the At least greatly reduce adhesive dispersions. Furthermore, the formulations without glycerin show a reduced initial adhesion.

In a second series of comparative experiments, the proportion of glycerol in the polychloroprene dispersions according to the invention was varied and the influence of the glycerol fraction on the adhesive properties was investigated at -20 ° C. Table 8 summarizes the properties of a polychloroprene-based adhesive at glycerine levels of between 5 and 40 weight percent. The buffer system consists of citric acid in addition to the glycerine, which is present in total at 0.378% by weight.

The initial liability is rated on a subjective scale of 1-10, with no initial liability rated at 1. A useful adhesive usually has values in the range 4-6 (satisfactory - very good).

Table 8:

Table 9 also shows the properties of a polychloroprene-based adhesive. In addition, however, there is an acrylate dispersion. The adhesive properties of the dispersion adhesive with glycerol contents between 5 and 40 wt .-% are summarized. In addition to glycerol, the buffer system also contains citric acid, which is present in a proportion of 0.378% by weight.

Table 9: Wt% Glycerin Initial adhesion Frost-thaw stability at -20 ° C

5 6, peel off glue no

10 6, threading no

15 5.5, not correctable no

20 5 no

25 4.5 yes

30 3.5 - 4 yes

35 3 yes

40 2 yes

Both series of tests show that formulations with very small glycerine levels do not have a freeze-thaw stability at -20 ° C. So z. B. in the formulations with a glycerol content of 5 wt .-% found during thawing consistently residues, which at least greatly reduce the quality of the adhesive dispersions. The initial liability, however, remains at a high level.

For adhesive formulations with a glycerol content below 22 wt .-%, especially in the range 14-22 wt .-%, but also in the range of 8-14 wt .-%, you will find limited frost-thaw stabilities. This means that these adhesives can be used at low frost, z. At -10 ° C. Initial adhesion is not affected by these glycerin levels.

In the particularly preferred range of 22-30% by weight of glycerol there is a good freeze-thaw stability at -20 ° C. and at the same time a good initial adhesion.

In practice, particularly preferred are glycerol contents of 12-40 wt .-%, in particular 14-30 wt .-%.

Adhesives with glycerol contents above 30 wt .-%, especially in the range 30- 40 wt .-% also have a good freeze-thaw stability. However, in these formulations, the initial adhesion is limited, the setting of the adhesive is slowed down. Such an adhesive offers advantages at very low temperatures (below -20 ° C), even if the bonding process takes longer. An even more extreme frost-thaw stability can be achieved by glycerol levels of 40-50 wt .-%. The disadvantage, however, is that such a formulated adhesive has a poor initial adhesion and also dries very slowly. With even higher glycerine levels, the adhesive properties are no longer sufficient. In further experiments, the necessary for a certain temperature glycerol content was determined.

For an adhesive according to the first adhesive composition of the invention based on polychloroprene, a very good freeze-thaw stability at -15 ° C. can be achieved by glycerol contents of 20% by weight. For frost-thaw stability at lower temperatures (-20 ° C, -25 ° C and -36 ° C), however, proportions of more than 25 wt .-% are necessary. The adhesives are very stable.

For an adhesive based on polychloroprene and acrylate, a freeze-thaw stability at -15 ° C. can likewise be achieved by a glycerol content of 20% by weight. However, thawing can not be completed completely without residue. This is only possible with a glycerol content of about 25% by weight. For a frost-thaw stability at lower temperatures (-20 ° C, -25 ° C or -36 ° C), however, proportions of more than 25 wt .-% are necessary. Coagulates are already formed at temperatures below -25 ° C.

The abovementioned exemplary embodiments or adhesive dispersions are only to be understood as illustrative examples, which can be modified as desired within the scope of the invention.

In the case of the first five adhesive dispersions, it is possible, for example, to additionally mix in acrylates and / or to dispense with emulsifiers, thickeners, biocides, plasticizers, defoamers, stabilizers and / or substances for adjusting the viscosity or these by other substances, such as. B. called in general part of the description to replace. It is also possible to provide instead of or in addition to the acids mentioned another acidic compound, for. As citric acid, tartaric acid, ascorbic acid, maleic acid or its anhydride, malic acid, amino acids such. As glycine, monosodium dihydrogen phosphate and / or carbonic acid. In the novel adhesive dispersions 6 and 7 based on polychloroprene and acrylate z. B. on the Acrylates, stabilizers, emulsifiers, plasticizers, thickeners and / or viscosity adjustment substances are dispensed with. It is also possible, these components by other substances such. B. called in general part of the description to replace. Instead of or in addition to the citric acid can also by another acidic compound, eg. As tartaric acid, ascorbic acid, maleic acid or its anhydride, malic acid, amino acids such. As glycine, monosodium dihydrogen phosphate and / or carbonic acid can be used. It is also conceivable to admix the novel adhesive dispersions, for example polyurethanes.

Fillers, in particular CaC0 ₃ , ZnO, MgO, Ti0 ₂ , Zr0 ₂ and / or talc, may also be added to all of the novel adhesive dispersions. Also possible is the addition of additional components from the series dyes, wetting agents, resin, UV absorbers, defoamers and / or biocides.

In summary, it should be noted that advantageous adhesives based on polymer dispersions have been created, which are characterized by high initial adhesion and stability. Due to their high stability, the adhesives can be easily designed as single-component adhesives and, in addition, can be adjusted to achieve frost-thaw stability. The latter, in particular, can significantly reduce transport and storage costs.

Claims

claims

1. Adhesive based on a polychloroprene dispersion with a buffer system comprising at least one acidic compound and glycerol, for activation and stabilization of the adhesive, characterized in that glycerol based on the total weight of the adhesive in the proportion of 8 - 50 wt .-% is present.

2. The adhesive of claim 1, wherein glycerol based on the total weight of the adhesive in the proportion of 14 - 40 wt .-%, particularly preferably 22 - 30 wt .-% is present.

3. Adhesive according to one of claims 1 - 2, wherein the polychloroprene dispersion additionally contains polyacrylates, in particular acrylic acid ester copolymers, styrene acrylate copolymers and / or mixtures thereof.

4. An adhesive according to any one of claims 1-3, wherein the polychloroprene dispersion additionally contains polymers and / or copolymers of vinyl acetate, ethylene vinyl acetate, vinyl butyral and / or urethane.

5. An adhesive according to any one of claims 1-4, wherein the at least one acidic compound has a pK _s value of 2-10.

6. An adhesive according to any one of claims 1-5, wherein the at least one acidic compound comprises citric acid, tartaric acid, ascorbic acid, maleic acid, maleic anhydride, malic acid, amino acids, in particular glycine, monosodium dihydrogen phosphate and / or carbonic acid.

7. An adhesive according to any one of claims 1-6, wherein the at least one acidic compound based on the total weight of the adhesive dispersion over a proportion of 0.01 to 10 wt .-%, in particular 0.1 to 1.5 wt .-%, has.

8. Adhesive according to one of claims 1 - 7, wherein a weight ratio of glycerol to at least one acidic compound in the range of 0.8 - 500, in particular 5 -

300, more preferably 10-100.

9. Adhesive according to one of claims 1-8, wherein a pH of the adhesive in the range of 5-9, preferably in the range of 7-9.

10. An adhesive according to any one of claims 1-9, comprising at least one emulsifier, wherein the at least one emulsifier, in particular a polyglycol ether,

Sodium lauryl sulfate and / or methyl vinyl ether / maleic anhydride copolymer includes.

1 1. An adhesive according to any one of claims 1-10, comprising a plasticizer, in particular one or more representatives from the series Acetyltributylcitrat, benzoates and / or Terephtalsäuredialkylester.

12. An adhesive according to any one of claims 1-11, containing fillers in the form of CaC0 ₃ , ZnO, MgO, Ti0 ₂ , ZrO _z and / or talc.

13. An adhesive according to any one of claims 1-12, wherein one or more additional components from the series thickeners, dyes, wetting agents, resin, UV absorbers, defoamers and / or biocides are present.

14. Use of a buffer system comprising at least one acidic compound and glycerin for activating and stabilizing an adhesive based on a Polychloroprene dispersion, wherein glycerol based on the total weight of the adhesive dispersion has a content of 8-50 wt .-%.

15. Use of a buffer system according to claim 14, wherein glycerol, based on the total weight of the adhesive dispersion, has a fraction of 14-40% by weight, particularly preferably 22-30% by weight.